1. Field of the Invention
The present invention relates to a color adjustment method, a color adjustment apparatus, a color conversion definition editing apparatus, an image processing apparatus, a program, and a computer readable storage medium in which the program is stored. More particularly, it relates to a color adjustment function of a color image or an editing function of a color image color conversion coefficient in a color image processing apparatus or a color image color conversion coefficient generation apparatus. Specifically, a technique for converting a color of a color space coordinate system into another color on the same color space in an apparatus such as a digital color copying machine, a printer, a printer driver, a printer controller, a color FAX or a color display including color adjustment as a part of its function, a color conversion generation apparatus called a profiler for generating a color conversion coefficient (profile), or an apparatus for editing or adjusting a profile.
2. Description of the Related Art
There is a color adjustment function as one of functions of adjusting a digital color image. In this color adjustment function, there is often a case that it is difficult to make desired conversion generally when relevance to perception about color such as hue, saturation and lightness of a person is low. In reverse, a computer graphics (CG) designer for directly handling RGB or a print-related designer for directly handling CMYK mainly, etc. are accustomed to editing of the RGB or CMYK on a routine basis and there is also a case that editing can be performed in RGB color space or CMYK color space conversely as intended. Thus, depending on object fields, color space for color adjustment ranges widely.
Also, color adjustment can be broadly divided into total region color adjustment influencing a color space total region to which a digital color image belongs and partial color adjustment influencing only its partial color space. A concrete example of the total region color adjustment includes contrast enhancement, saturation enhancement and color balance adjustment, and a concrete example of the partial color adjustment includes an example of adjusting only a flesh color.
As the art related to the total region color adjustment, for example, a technique in which an RGB color signal from a scanner is converted into an HLS color signal every hue (H), lightness (L) and saturation (S) using an independent lookup table and the HLS color signal after the conversion is inversely converted into the RGB color signal and thereby color adjustment and color modification are made in the form adapted to perception of a person is disclosed in JP-A-64-16658.
However, this technique is a technique for making total color adjustment or color modification, and it is difficult to adjust only a local color in great demand for a person within color space, for example, to reproduce only a color such as a flesh color which a person has as an image, the so-called memory color to a preferable color.
On the other hand, as the art related to the partial color adjustment, for example, a technique in which a color conversion section is constructed of a developed color system unit, a memory color adjustment unit and an inverse developed color system unit and an RGB color signal from a scanner is converted into a color signal such as hue, saturation and lightness fit for a sense of a person and also only an object region of a memory color such as a flesh color is converted by an object region specification table so that discontinuity does not occur between a region outside an object and the object region and the color signal after the conversion is inversely converted into the RGB color signal and thereby color adjustment is made independently of masking is disclosed in JP-A-2-96477.
This technique disclosed in JP-A-2-96477 is a technique for making smooth local color adjustment by multiplying the movement amount by a function of a distance from the center of movement (the center of gravity) as weight, but lightness is handled independently of chromaticity (hue, saturation), so that there is a disadvantage that it cannot be applied to color space in which lightness is not independent like RGB space. That is, a movement distance and an influenced range are in a dependent relation when a condition that gradation inversion is not caused is added, and the amount of local color adjustment is determined by the center of gravity, a movement vector and a weight function (a distance from the center of gravity and an applied range), so that it is difficult to be applied to a system other than a lightness and chromaticity separation system. Also, a method for increasing an object region specification table must be adopted for adjusting plural colors and there is a demerit that a load on hardware increases.
Also, a technique in which a representative color representative of a color of an adjustment object region is determined based on image data showing a color of each pixel included in the adjustment object region extracted from a color image and a fundamental vector showing movement in color space from the representative color to a target color is obtained according to an input of a target color targeted for a color after adjustment of the adjustment object region and image data included in the adjustment object region is moved in the color space according to a direction and a distance shown by the fundamental vector is disclosed in Japanese Patent No. 3009934 (JP-A-4-321182). Specifically, it is the technique in which a representative color representative of a color of an adjustment object region is determined and a movement vector is obtained from a target color after adjustment and distance weight is obtained from a distance between a color of each pixel and the target color and the movement amount is obtained by multiplying the movement vector by the weight coefficient.
Also, a technique in which partial color adjustment is made so that it does not become discontinuous with the outside of a partial range by specifying each of the color coordinates before and after conversion and ranges of a sphere or an ellipsoid, etc. containing them is disclosed in JP-A-9-214792. This technique discloses a technique for solution by determining weight of movement by a Euclidean distance from the center of gravity in color space such as RGB color space or L*a*b* color space with respect to a problem that lightness is independently handled (distance calculation is independently performed in lightness and chromaticity) in the technique described in JP-A-2-96477.
According to this technique, an arbitrary color of an arbitrary color space coordinate system can be converted into another color on the same color space so that discontinuity does not occur in the boundary of a color outside an object and also, plural colors can be converted into other colors respectively and further in that case, not only when a weight coefficient function is fixed with respect to the respective colors but also when the weight coefficient function is switched, its weight coefficient function can be implemented by a one-dimensional lookup table, so that there is an advantage that a load is not applied to hardware.
However, this technique has flexibility higher than that of the technique described in JP-A-2-96477, but the fact that a movement distance and an influenced range are in a dependent relation when a condition that gradation inversion is not caused is added remains unchanged.
Incidentally, advantageous features common to JP-A-2-96477, Japanese Patent No. 3009934 (JP-A-4-321182) and JP-A-9-214792 described above are that it moves from a color before adjustment to a color after adjustment inside an adjustment object region, and conversion is made so that it does not become discontinuous in the boundary between the adjustment object region and the outside of the adjustment object region.
By the way, the conventional art described above focuses attention on only continuity between an adjustment object region and the outside of the adjustment object region in color reproduction when partial color adjustment is made, and does not take inversion or continuity of a tone into consideration. Therefore, when the conventional art is applied to make the partial color adjustment, for example, unpictorial image reproduction (perceived by eyes of a person) resulting from discontinuity (inversion or sudden change) of a tone occurs. More specifically, for example, when it is considered that a desired color coordinate before adjustment inside color coordinate space is adjusted to a color coordinate after adjustment, a disadvantage that gradation inversion occurs unless a color adjustment region containing the color coordinate before adjustment and the color coordinate after adjustment is assumed occurs.
Also, the conventional art described above has no flexibility of arbitrarily specifying a color coordinate before adjustment, a color coordinate after adjustment and an adjustment object region, and the minimum adjustment object region is determined by the color coordinate before adjustment and the color coordinate after adjustment. There is qualitatively constraint that the adjustment object region must be taken wider as a distance between the color coordinate before adjustment and the color coordinate after adjustment increases.